Associations between Dissolved Uranium, Nitrate, Calcium, Alkalinity, Iron, and Manganese Concentrations in the Edwards-Trinity Plateau Aquifer, Texas, USA

Abstract

Dissolved uranium, nitrate, calcium, alkalinity, iron, and manganese concentrations were compiled from samples collected at 108 water wells between 2010 and 2016 in the Edwards-Trinity Plateau Aquifer of southwestern Texas. Sampled wells ranged from 19 m to 85 m deep, with a median depth of 77 m. Uranium concentrations ranged from <1 μg/L to 154 μg/L, with a median concentration of 19 μg/L. In 31 wells, uranium concentrations exceeded the drinking water standard of 30 μg/L. Based upon Spearman rank correlation, at a significance level of 0.01, significant positive associations were observed between uranium and both nitrate and calcium concentrations. In 40 wells sampled twice within the above time period, uranium concentrations decreased in 25 wells, increased in 13 wells, and did not change in two wells. The maximum concentration decrease and increase was 10 μg/L and 67 μg/L, respectively. Change in uranium concentration was significantly, positively correlated with change in nitrate and calcium concentration.